1. Field of the Invention
The present invention relates to a circuit board transportation device for transporting a circuit board, a circuit board working apparatus for executing a predetermined operation on a circuit board transported to an operation position by a circuit board transportation device, and a conveyor belt suitable for a circuit board transportation device. Examples of the operation carried out by the circuit board working apparatus include surface mounting, circuit board inspection, application of coating, printing, and reflow of a circuit board mounted with parts.
2. Background Art
In a circuit board working apparatus such as a surface mounter, a circuit board is carried into an operation position and then carried out of the operation position upon completion of an operation executed thereon. For the purpose of transporting a circuit board in this manner, the circuit board working apparatus is equipped with a circuit board transportation device. The circuit board transportation device described in, for example, Japanese Patent Application Publication No. 2009-289780 (FIG. 3) has a pair of right and left conveyor belts. This circuit board transportation device has a conventional general flat belt as each of these conveyor belts. Each conveyor belt supports a circuit board by its internal section in a cross direction (lateral direction) and moves (runs) by being driven by a drive motor, to transport the circuit board. Also, guide members are provided corresponding to the conveyor belts respectively. Each of the guide members covers from above an outer end of the corresponding conveyor belt in the cross direction. The guide members have upright guide surfaces on the inside thereof in the cross direction, and take advantage of these guide surfaces to guide side end surfaces of the circuit board transported by the conveyor belts, to keep the circuit board during transportation in a fixed position. This circuit board transportation device stabilizes transportation of a circuit board in this manner. This circuit board transportation mode described in Japanese Patent Application Publication No. 2009-289780 is referred to as “prior art 1.”
Japanese Patent Application Publication No. 2000-264414 (FIGS. 1, 2, 4 and 5) describes two types of circuit board transportation devices different from the one described in prior art 1. One of the circuit board transportation devices (shown in FIGS. 4 and 5) has conveyor belts configured by flat belts, wherein a lower surface of a circuit board is supported in the entire cross direction (lateral direction) of the conveyor belts. A pair of right and left guide members are disposed on the outside of the right and left conveyor belts respectively to guide the circuit board in such a manner as to sandwich it from the outside of the conveyor belts. Such a circuit board transportation mode is referred hereinafter to as “prior art 2.”
The other circuit board transportation device described in Japanese Patent Application Publication No. 2000-264414 (shown in FIGS. 1 and 2) transports a circuit board by using a conveyor belt provided with a guide function. This circuit board transportation device is referred hereinafter to as “prior art 3.” In this prior art 3, inner ends of the conveyor belts in the cross direction support a lower surface of a circuit board and function as transporting units for transporting the circuit board. In each of these conveyor belts, an outer end in the cross direction that is linked to each inner end (transporting unit) projects upward, and this projection functions as a guide portion by holding the outside of the circuit board.
Although these types of circuit board transportation modes have conventionally been developed, applicability thereof to circuit board working apparatuses is limited, leading to a problem with versatility.
In prior art 1, for instance, each of the guide members covers from above the outer end of the conveyor belt in the cross direction, and a gap is formed between the lower surface of each guide member and the corresponding conveyor belt and expands toward the circuit board. When a circuit board to be transported is relatively thin (“thin circuit board”), the thin circuit board enters such a gap and becomes stuck therein. Thus, prior art 1 can only transport a circuit board that is sufficiently thicker than the gap (“thick circuit board”).
Prior art 2, on the other hand, has an impact on the width that allows leeway for the conveyor belt to support the circuit board (support width), because the lower surface of the circuit board is supported in the entire cross direction of the conveyor belt. In other words, while the width of each conveyor belt needs to be made equal to or less than the support width, when parts are mounted on the circuit board the support width corresponding to the surface mounted with the parts becomes extremely narrow. This situation reduces the cross-sectional area of the conveyor belt, making it difficult to secure sufficient belt strength. Consequently, transporting a relatively heavy circuit board stretches the conveyor belt, making it difficult to transport the circuit board correctly. This also might cause breakage of the belt. For these reasons, prior art 2 can only transport relatively light circuit boards.
In prior art 3, each guide portion for guiding a circuit board is linked to a corresponding transporting unit and projects upward. Because a conveyor belt is normally made of a flexible material, each guide portion undergoes a lateral load from the circuit board each time when guiding the circuit board in the cross direction. Such repeated application of the lateral load to each guide portion repeatedly applies shear force to the part or so-called joint where the guide portion and the transporting unit are connected to each other, leading to problems such as cracking of the joint of the guide portion and breakage of the guide portion. As a result, the circuit board cannot be transported stably.